Recently, with the rapid development of semiconductor technology, efforts have been made to mount as many semiconductor chips as possible in a given area. As an example, a resin sealed-type semiconductor package in which two semiconductor chips are mounted is illustrated in FIG. 1.
FIG. 1 is a longitudinal cross-sectional view showing the construction of the resin sealed-type semiconductor package according to the conventional art. As shown in this drawing, the resin sealed-type semiconductor package includes: first and second semiconductor chips 1, 1' each disposed to have their chip pads (not illustrated) facing each other with a space therebetween; bumps 3, 3' formed on each chip pad of the first and second semiconductor chips 1, 1', respectively; a plurality of first internal leads 4 one end of each of which is connected to a corresponding bump 3 of the first semiconductor chip 1; external leads 5 extended from the other end of the first internal leads 4; a plurality of second internal leads 4' one end of each of which is connected to a corresponding bump 3' of the second semiconductor chip 1' and the other end of each of the second internal leads 4' is connected with a corresponding one of the first internal leads 4; and a molding unit 6 sealing the first and second semiconductor chips 1, 1' and the first and second internal leads 4, 4'.
The fabrication of the conventional resin sealed-type semiconductor package having the above-described construction will now be described in detail.
The first internal leads 4 are attached (using the bumps 3) to each corresponding pad (not illustrated) formed on the first semiconductor chip 1. The second internal leads 4' are attached (using the bumps 3') to the corresponding pads formed on the second semiconductor chip 1'. According to the bump bonding method: the bumps 3, 3' are located on each pad of the first and second semiconductor chips 1, 1', respectively; the first and second internal leads 3, 3' are attached to the upper surfaces of the bumps 4, 4'; and heat is applied thereto to bond the pads, the bumps 3, 3' and the internal leads 4, 4' together.
Next, the first and second internal leads 4, 4' are respectively attached to the first and second semiconductor chips 1, 1'. The second internal leads 4' of the second semiconductor chip 1' are located on the corresponding first internal leads 4 of the first semiconductor chip 1. Then, using a laser, a bonding process is performed to attach the internal leads 4, 4' to each other. Then, a predetermined area, in which are located the first and second semiconductor chips 1, 1' and the first and second internal leads 4, 4', is sealed with an epoxy resin to form the molding unit 6. The external leads 5 are formed to extend or protrude from the first leads 4 out of the molding unit 6, according to the purpose of a user. This completes the formation of the resin sealed-type semiconductor package.
However, there are some problems with the resin sealed-type semiconductor package. There is a limit to the mountable number of semiconductor chips. The semiconductor package cannot be stacked for use. Moreover, the internal leads are bonded to pads of the semiconductor chips using the bump bonding method, which is an exacting process in comparison with the widely used wire bonding method and incurs a high production cost.